Nowadays, to improve viewability of images on the screen of a personal computer, an image region is subjected to highlighting. In such a highlighting process, in order to unhighlight a character region, it is necessary to judge whether the pixel of interest is a pixel included in a character.
The inventor performed judgment of a text region using the following method.
1) A histogram for y values of nine pixels, including the pixel of interest and eight pixels adjacent to the pixel of interest is prepared. 2) The total sum of the most frequent gray-level, the second most frequent gray-level, and the third most frequent gray-level are obtained. 3) The total sum is compared with a threshold. If the total sum is greater than or equal to the threshold, the region is judged as text; if the sum total is smaller than the threshold, the region is judged as non-text. 4) Based on the judgment result, a uniform average filter of 3 lines*5 pixels is superimposed to automatically adjust the intensity of image processing.
Patent Document 1 discloses an image processing device which can detect a thin line accurately and output a thinned image, such as a black character, with high quality.